In one aspect, this invention relates to a magnetically operated liquid level indicator of the kind having a magnetized float which moves as the level of liquid changes, and having a plurality of magnetized indicator elements disposed one above the other and past which the magnetized float travels as the liquid level rises or falls, the indicator elements being rotatable under the influence of the magnetized float.
One of the shortcomings of prior art level indicators of this type is an upper practical limit to the size of the indicator elements. Once the indicators reach a certain size, the magnetic attraction between them is difficult to overcome with the float. Prior art indicators have often been limited to an indicator width of about one inch. Where the level indicator is disposed far above ground level, it is difficult to read the level indicated by such small indicator elements from the ground. A liquid level indicator which has wide indicator elements would be very desirable.
Another shortcoming of prior art indicators is a practical upper limit to operating temperature. Where the indicator is used to measure the liquid level of hot fluids, exposure to excessively hot temperatures can lead to degaussing of the indicator elements, and malfunctions of the level indicator. As many refining, chemical and petrochemical processes operate at fluid temperatures of up to 1100 degrees Fahrenheit, a liquid level indicator which does not malfunction after exposure to such temperatures would also be desirable.
Other prior art indicators have used a multi piece indicator element construction in an attempt to overcome the strong attraction between long magnetic indicator elements, such as by using a small magnet in a longer non-magnetic flag. However, multi piece indicator elements are expensive to fabricate, and are also subject to corrosion where dissimilar materials have been used. An indicator element which is of unitary construction and is formed from a highly corrosion resistant material would further be very desirable.
It is an object of this invention to provide a liquid level indicator with long indicator elements which can be easily viewed from a distance.
It is another object of this invention to provide a liquid level indicator where the indicator elements are narrow and closely spaced, so that the indicated level can be determined with good resolution.
It is a further object of this invention to provide a liquid level indicator which is useful and reliable up to an operating temperature of 1100 degrees Fahrenheit.
It is a further object of this invention to provide a liquid level indicator which utilizes indicator elements which are of inexpensive unitary construction and are formed from a highly corrosion resistant material.
In one embodiment of the invention, there is provided an indicator flag which can be used in a liquid level indicator of the magnetic type. The indicator flag is longitudinally elongated and is formed from a magnetizable composite material. The flag has a first end, a second end, a longitudinal axis, and a generally rectangular cross section transverse to the longitudinal axis. A borehole extends along the longitudinal axis of the flag from the first end to the second end. The first end of the flag defines a generally planar first end surface first portion onto which the borehole opens and a generally planar first end surface second portion which is longitudinally spaced from the first portion surface. A generally cylindrical first end surface third portion is radiused around the borehole and connects the first portion and the second portion. The borehole permits the flag to be rotatably mounted to a mounting pin, which lessens the risk of binding. The radius permits the flag to be sufficiently closely mounted to a rotation stop so that the flag faces are near vertically positioned adjacent to the stop, without the flag binding against the stop as it rotates. The second end surface permits the flag to rotate past a rotation stop.
In another embodiment of the invention, a liquid level indicator is formed from a frame, a plurality of parallel pins, and a plurality of magnetic slats, which are preferably in the form of the just described flags.
The frame is longitudinally elongated and channel shaped and is formed of a nonmagnetic material. The frame is defined by a first sidewall, a second sidewall parallel to the first sidewall, and a bottom wall connecting a bottom end of the first sidewall with a bottom end of the second sidewall. The frame has a longitudinal axis.
The plurality of parallel pins extends from the first sidewall to the second sidewall. The parallel pins are positioned parallel to the bottom wall and are longitudinally spaced apart from each other and the bottom wall. The pins extend normally to the longitudinal axis of the frame.
The plurality of magnetic slats is mounted to the parallel pins, one slat per pin. Each magnetic slat has a thickness, a height which is greater than the thickness, and a length which is greater than the height, and is positioned on a pin with its length extending parallel to the pin for pivoting movement around the pin. Normally, the height of each slat extends parallel to the longitudinal axis of the frame. Each slat has a magnetic axis parallel to its height, a first face having a first color, and an opposite second face having a second color which is optically discernable from the first face. Each slat has a length which is at least three times its height to facilitate viewing of the slat face.
The parallel pins are spaced apart a first distance which is slightly greater than the height of the slats, so that adjacent slats are aligned with each other in an edge to edge relationship due to mutual magnetic attraction and have sufficient clearance therebetween to permit each slat to pivot without mechanical interference from adjacent slats.
In another embodiment of the invention, there is provided a process for magnetizing pieces of magnetizable bar stock having a rectangular cross section. To carry out the process, a passage of rectangular cross section is formed in a mass of magnetically permeable material. The mass is positioned between a pair of magnetizing poles with the passage extending normally to an axis drawn between the poles. Pieces of bar stock having a rectangular cross section closely corresponding to the rectangular cross section of the passage are passed through the passage, under conditioned so that the magnetizing poles exert sufficient magnetizing force to magnetize the pieces of bar stock. Each piece of bar stock has a thickness, a height which is greater than the thickness, and a length which is greater than its height, and is passed through the passage so as to induce magnetism in a direction parallel to its height in an amount which in the range of from about 5% to about 50% of a saturation limit of the magnetizable material.
Magnetizing the flags to beneath the saturation limit makes feasible the use of closely spaced, long one-piece ceramic magnets as the indicator flags. Were the ceramic magnets fully magnetized, as taught by the prior art, the attractive forces between the long indicator flags would be too strong to be overcome by the magnetized float. The weakly magnetized magnets can also be subjected to temperatures which would cause degaussing of fully magnetized indicator flags without loss of function.